1. Field of the Invention
The present invention relates to an exposure apparatus for exposing a substrate to a light.
2. Description of the Related Art
A projection optical system which constitutes an exposure apparatus needs to achieve a good optical characteristic such as various kinds of aberrations. Therefore, the optical characteristic of the projection optical system is measured and an adjusting amount (a correction amount) for adjusting the optical characteristic is calculated based on the measured optical characteristic to perform an appropriate adjustment based on the calculated adjusting amount. The optical characteristic of the projection optical system changes in proportion to the adjusting amount of each element (for example, an optical element such as a lens) which constitutes the projection optical system. Japanese Patent Laid-open No. 2002-367886 discloses a technology of determining the adjusting amount of each element using a linear programming.
The optical characteristics of the projection optical system also contain a characteristic represented by a weighted sum of squares of a wavefront aberration coefficient at each point in an image plane (an exposure region), as is the case with a square of a wavefront aberration RMS value. Japanese Patent Laid-open No. 2005-268451 discloses a technology that optimizes a primary estimation value (an optical characteristic value that is represented by a linear function of an adjusting amount of each element) and a quadratic estimation value (an optical characteristic value that is represented by a quadratic function) in a balanced manner. Japanese Patent Laid-open No. 11-176744 and International Publication No. 02/054036 disclose different technologies of adjusting the optical characteristic of the projection optical system.
However, a conventional method of adjusting the projection optical system calculates an adjusting amount as an optimized solution so that an adjustment target (an objective function) in a predetermined constraint range is minimized. Therefore, the adjusting amount of the projection optical system can be freely changed in the constraint range. However, in the adjustment method, there is a possibility that a large adjusting amount is necessary in order to improve a minute adjustment target that has a comparatively small influence even if there is a solution where the adjustment target is equal to or less than a target value with a small adjusting amount. If the adjusting amount becomes large, an adjustment error increases in proportion to the adjusting amount and an adjusting amount margin in other adjustment processes cannot be obtained. Therefore, the achievement of the targeted optical characteristic with a smaller adjusting amount is required.